Ocean Forecast for the Western Indian Ocean

(i)Prepare ocean state forecasts for the Western Indian Ocean region for the September-December 2014 period

(ii)Assess potential impacts of the predicted ocean state on climate in the region, and also on the marine sector

(iii)Review available predictions on the development of El Niño and IOD events and their possible impacts on the ocean state and climate in the region (based on documented experiences with previous incidents of the events)

The ocean plays a crucial role in seasonal, interannual and longer time fluctuations in climate, mainly through ocean- atmosphere coupling. The dominant coupled ocean-atmosphere interaction, the El Nino-Southern Oscillation (ENSO) anomaly patterns in Pacific Ocean Sea-Surface Temperatures (SSTs), has a predominant influence on the inter-annual variability of the global climate, including East Africa’s climate (Indeje et al., 2000). The Indian Ocean SSTs through the ocean-atmosphere coupled mode of variability, the Indian Ocean Dipole (IOD), also plays a crucial role in the inter-annual variability of East Africa’s climate.

The IOD can explain some climatic extremes over the East African region, which could not be explained by ENSO (Saji et al., 1999). The inter-annual variability of East Africa’s climate is mainly associated with perturbations in the global SSTs, especially over the equatorial Pacific and India Ocean basins, and the Atlantic Ocean to some extent (Mutai et al., 1998; Indeje et al., 2000; Saji et al., 1999; Goddard and Graham, 1999). The modulation on SST is largely due to oceanic processes, mainly through vertical and horizontal advection and upwelling (Behera et al., 1999; Murtugudde et al. 2000).

Recent studies show it is insufficient to rely on prediction of SST in the Pacific as an indicator of ENSO uptake over the Indian Ocean. Even if the strength of the Pacific ENSO is accurately predicted, the resulting pattern of rainfall and storm events around the Indian Ocean varies markedly. For example the 1982/83 and 1997/98 El Nino events produced very different impacts. The former event induced devastating drought in southern Africa and Australia, yet the more recent episode produced floods in East Africa and drought across Indonesia: an east–west dipole pattern. It can be expected that local climatic conditions around the Indian Ocean will depend not only on remote forcing, but also on local patterns of SST and the manner in which the atmosphere responds.

Studies suggest that the major systems controlling East African rainfall are primarily forced by the Indian Ocean processes. The processes in the Pacific Ocean play a secondary role (Hastenrath and Polzin, 2003). However, the details of the interaction between the ocean and the atmosphere in the Greater Horn of Africa (GHA) are not fully understood. Whereas the SSTs in the Indian Ocean basin play a crucial role in the region’s climate, the oceanic processes controlling the evolution of the Indian Ocean SSTs are not well understood.

In the West Indian Ocean a number of countries can benefit from ocean applications. Most of the economic activities in this region of the Indian Ocean for example shipping and fishing activities along the coasts of East Africa and the adjacent island states require reliable ocean state forecasts which include oceanographic components. Reliable and timely seasonal forecasts of the ocean state is vital to the shipping and offshore industries, ports and harbours, to safeguard operations and trade,facilitate coastal design and management, and permit optimal exploitation of fisheries resources. Therefore, forecasts of the ocean state will assist in reducing the severity of the impacts of extreme ocean events like extreme waves and tropical cyclones. In some parts of the region, cyclones cause heavy swells which cause significant rises in sea levels that affect coastal infrastructures such as roads and settlements, undermine beach stability, and cause vertical scouring (Ragoonaden 1997). Seasonal forecasts of the ocean state will also enhance the accuracy of information given to policy and decision makers which will assist in planning and mitigation of adverse impacts of oceanic events.

The availability of good disaster management information will provide guidance on effective ways in addressing the vulnerability of sensitive socioeconomic sectors and sustainable resilience of the coastal comunities. The workshop will also enhance the skills of the participants in ocean data management, sea state forecasting and modelling and hence build capacity for the WIO region.

The results of the workshop will be presented to the 38th Climate Outlook Forum for the Greater Horn of Africa (COF-38), which is scheduled to meet in Addis Ababa, Ethiopia in the last week of August 2014, and the pre-COF 38 Climate experts meeting.